One of the more recent issues to occur between Ahl as-Sunnah wa al-Jamāʾah & Ahl al-Bidʾah wa al-Hawā is the statement of The Prophet ﷺ in which he said:
The Jews divided into seventy-one sects, the Christians divided into seventy-two sects, and this Ummah will divide into seventy-three sects; all of them are in the fire except one.
It was then said:
Who are they, O Messenger of Allāh?
The Prophet ﷺ replied:
They are those upon what me and my companions are upon.
And in another wording, The Prophet ﷺ replied:
the Jamāʾah.Musnad Aḥmad #8404, Sunan ibn Mājah #3992, Sunan Abū Dāwūd #4596, Jāmiʿ at-Tirmidhī #2640, Kitāb as-Sunnah #64, al-Mustadrak ʿala aṣ-Ṣaḥīḥayn 1/128, Kitāb ash-Sharīʿah #26, Musnad Abī Yaʿlā #3938, Sharḥ Uṣūl al-I’tiqād #148, al-Farq Bayna al-Firaq #3, Ṣaḥīḥ ibn Ḥibbān #6247, Sunan al-Bayhaqī 10/208, al-Mu’jam al-Kabīr 19/376, Musnad ash-Shāmīyyīn 2/108, Sunan ad-Dārimī #2518, al-Ḥujjah fī Bayān al-Muḥajjah #16, Sharaf Aṣḥāb al-Ḥadīth #35, al-Mu’jam al-Awsaṭ #7840, al-Mu’jam aṣ-Ṣaghīr #724, Silsilah al-Aḥādīth aṣ-Ṣaḥīḥah #204, al-Bidaʾ wa an-Nahī ʿAnhā #85, Aḥkām al-Qurʾān 3/432, al-Mughnī ʿan Ḥaml al-Asfār 2/885 | Ṣaḥīḥ to Imām al-Hākim an-Nishāpurī, Imām adh-Dhahabī, Imām ibn Ḥibbān, Imām at-Tirmidhī, Abū Bakr ibn al-ʿArabī, Shaykh al-Albānī, Shaykh Zubayr ʿAlī Zay, and others
Due to the veracity of the statement, “all of them are in the fire except one” and the one being the Saved Sect, Ahl al-Bidʾah wa al-Hawā have put forward many doubts & weak arguments against the Ḥadīth such as attemping to discredit it’s authenticity, though by the aid & decree of Allāh ﷻ it has been narrated in numerous books of Ḥadīth & authenticated by a large number of scholars.
WHO ARE THE JAMĀʾAH?
ibn Masʾūd رضي الله عنه said: “al-Jamāʾah is whatever agrees with the truth, even if you are alone in that.” 
Isḥāq ibn Rāhwayh رحمه الله (d. 238 AH/853 CE) said: “If you asked the (ignorant) people about as-Sawād al-Aʾẓam (Main body of Muslims), they will say it is a collective of people, but they do not know that the Jamāʾah is the scholar who holds fast to the narrations of The Prophet ﷺ and his path. So whoever is with him and follows him, then they are the Jamāʾah.” 
Shaykh al-Islām ibn Taymīyyah رحمه الله (d. 728 AH/1328 CE) said: “The characteristc of the Saved Sect is that they adhere to the Sunnah and the Jamāʾah, and they are the overwhelming majority, as-Sawād al-Aʾẓam. As for the rest of the sects, then indeed they are people who adhere to odd ideas, division, Bidʾah (in the religion), and following lowly desires; none of these sects have reached closeness to the saved sect in number, some reaching only a very small number.
The distinguishing sign of these groups is that they split off from the Book (al-Qurʾān), Sunnah, and Ijmāʿ. Whoever speaks with the Book, Sunnah, and Ijmāʿ, then they are from Ahl as-Sunnah wa al-Jamāʾah.” 
Shaykh Ṣāliḥ al-Fawzān حفظه الله said: “Ahl as-Sunnah wa al-Jamāʾah are those who adhere to the Sunnah of The Messenger of Allāh ﷺ, those are Ahl as-Sunnah. al-Jamāʾah are those who are united upon the truth without being divided as stated by Allāh ﷻ:
وَٱعۡتَصِمُواْ بِحَبۡلِ ٱللَّهِ جَمِيعٗا وَلَا تَفَرَّقُواْۚ
And hold firmly to the rope of Allāh all together and do not become divided.
– Sūrah Āli ʿImrān, ʾĀyah 103
They are united upon the truth without being divided over it or differing concerning it. Those are Ahl as-Sunnah wa al-Jamāʾah.” 
ARE ALL OTHER 72 SECTS CERTAINLY IN THE FIRE?
Shaykh al-Islām ibn Taymīyyah رحمه الله (d. 728 AH/1328 CE) said: “With the 72 sects, there are those from amongst them who are hypocrites and disbelievers internally, and those who are not hyprocites, but rather they are believers in Allāh and His Messenger ﷺ internally and not disbelievers, even though they have mistaken interpretations. Some amongst them may have that which are branches of hypocrisy, although not the kind of hypocrisy that would land the person guilty of it into the lowest levels of Hell.
Whoever says that all of the 72 sects are guilty of disbelief that removes them from the fold of Islām, then that person has opposed the Book, the Sunnah, the four A’Immah, and other than them. There is not amongst them anyone who declares all of the 72 sects to be disbelievers and they only declared some of them to be disbelievers due to some of the opinions that they (the sects) held.” 
The Permanent Committee for Research and Verdicts issued in a Fatwā: “What is meant by the term ‘Ummah’ in this Ḥadīth (of the 73 sects) is the Ummah of response which shall be divided into 73 sects, 72 of which are deviants who practice innovated religious practices that do not constitute apostasy. Each shall be tortured in accordance to it’s innovations and deviations except for those whom Allāh pardons and forgives, their final abode will be Paradise.
The only sect that will be safe is Ahl as-Sunnah wa al-Jamāʾah, (those) who adhere to the Sunnah of The Prophet ﷺ and hold fast to what he and his Companions, may Allāh be pleased with them all, were holding.” 
And Allāh knows best.
All praise is due to Allāh, may His peace & blessings be upon our final Prophet Muḥammad, his family, his companions, & all those who follow him in guidance.
 Mishkāt al-Maṣābīḥ (مشكاة المصابيح) by Imām at-Tibrīzī | Athar #173
 Ḥilyah al-Awliyā’ (حلية الأولياء) by Abū Nuʿaym al-Iṣfahānī | Volume 9, Page 239
 Majmūʾ al-Fatāwā (مجموعة الفتاوى) by Shaykh al-Islām ibn Taymīyyah | Volume 3, Page 346
 Itḥāf al-Qārī (إتحاف القاري) by Shaykh Ṣāliḥ al-Fawzān | Volume 1, Page 59
 Majmūʾ al-Fatāwā (مجموعة الفتاوى) by Shaykh al-Islām ibn Taymīyyah | Volume 7, Page 218
 Fatāwā Islamīyyah (فتاوى اسلامية) compiled by Muḥammad ibn ʿAbd al-ʿAzīz al-Musnad | Volume 1, Page 20
Ṣafīullāh Labīb ibn Salīm ʿAbd al-Malik
15th of Rabīʿ al-ʾAwwal 1444